Differences in UV-B tolerance among Spirodela punctata ecotypes

Ultraviolet-B (UV-B) radiation negatively impacts on plant growth and devel opment. Not all plants are UV sensitive: strong tolerance to UV-B radiation is particularly found among plants that naturally occur in areas of high W -B radiation. There is Limited knowledge about the mechanisms underlying su ch enhanced natural tolerance. In this study, we demonstrate strong differe nces in UV-B tolerance among Spirodela punctata ecotypes. Tolerance is visu alized as sustained photosystem II (PSII) activity and biomass accumulation in fronds exposed to UV-radiation. We find that the enhanced tolerance is constitutive and specific for UV-radiation stress, but it does not correlat e with well-characterized UV-adaptation responses like the accumulation of bulk UV-screening pigments in the epidermis, or increased oxygen radical sc avenging activity. (C) 1999 Elsevier Science S.A. All rights reserved.